The present invention relates to ultrasonic testing. Ultrasonic testing generally involves very short ultrasonic pulse-waves which are launched into materials to detect internal flaws or to determine the material type or characteristics of material. The nature of an ultrasound test requires that the ultrasonic probe come into complete contact with the surface of the test piece. The reason for this is that air between the probe and the test piece will give inconsistent and incorrect results in the test. Because the high frequency sound waves from the probe must travel into the test piece consistently across the entire test area there must not be any voids (air gaps) between the probe and the test piece. The very nature of an ultrasound test is to find unwanted voids in the test piece, without complete coupling between the test piece and the probe the test is of no use.
There are two primary methods of ensuring that the coupling between the probe 18 and the test piece are consistent. First, as shown in FIG. 1, coupling between the probe 18 and the piece 14 with a gel 16 and significant down-force of 30-40 PSI may be used. Second, as shown in FIG. 2, the test piece 14 and probe 18 may be immersed in a liquid bath 20. While both of these methods are very effective in many applications they are not generally effective in high volume production, or with delicate test pieces or parts that are non-immersible.
Other challenges arise when the test piece is large enough to require that the probe be moved to test the entire surface. Because the probe must remain in intimate contact with the surface of the test piece motion of the probe across the surface of the test piece becomes very difficult. The coupling mechanism (gel or elastomeric couplant) can be worn out or will not maintain a consistent coupling with the test piece. The combination of high down force and high friction makes moving the probe while scanning ineffective. The probe can be moved over the test piece in immersion applications (because it is not touching the piece) however that is not of any use in non-immersion applications.
Due to problems such as the test pieces in question being fragile, non-immersible and having non-uniform surfaces, ultrasonic testing has significant limitation. What is needed is a way to overcome these and other problems.